The invention relates to an electron tube having a semiconductor device for generating electrons, which device has a semiconductor body with a structure adjacent to a main surface in the semiconductor body, in which structure electrons to be emitted from the semiconductor body at the location of an emissive surface region can be generated by applying suitable voltages.
The invention more generally relates to a vacuum tube comprising a semiconductor device for influencing charged particles.
The electron tube may be used as a display tube or a camera tube, but it may alternatively be adapted, for example, for electrolithographic applications or electron microscopy.
The invention also relates to a semiconductor device for generating electrons or ions and for influencing their paths.
An electron tribe of the above-mentioned type is described in U.S. Pat. No. 4,303,930. In the semiconductor device, which is a "cold cathode", a pn junction is reverse biased in such a way that there is avalanche multiplication of charge carriers. Some electrons may then acquire as much kinetic energy as is necessary for exceeding the electron world, function. The emission of these electrons is simplified by providing the semiconductor device with acceleration electrodes or gate electrodes on an insulating layer located on the main surface, which insulating layer leaves an aperture at the location of the emissive region. Emission is still further simplified by providing the semiconductor surface at the location of the emissive region with a material reducing the work function such as, for example cesium.
If such a cathode is built into an electron tube, problems occur in the further manufacturing process. During the process, in a conditioning step known as spot-knocking, a number of grids in the tube acquire a high to very high voltage (100 kV to 30 kV) while the substrate and the gate electrode(s) of the semiconductor cathode are, for example grounded. During this spot-knocking operation, flashovers are produced so that the grid located closest to the cathode acquires a high voltage (approximately 10 to 30 kV) instead of a comparatively low voltage (approximately 100 V). Such a flashover may also occur during normal use.
The connection wires of the substrate as well as the gate electrodes cannot, however, be considered as purely ohmic connections, but have a given inductance. This results in a large voltage difference between the substrate and the gate electrode due to capacitive crosstalk between said grid and, for example this substrate. This voltage difference is also dependent on the inductances of the connection wires, the resistance of, for example the material of the gate electrode and the duration of the flashover. Usually, this difference is, however, so large that there is a destructive breakdown of the insulating layer between the gate electrode and the subjacent substrate. As a result, electron tubes comprising this type of cold cathodes are often rejected, notably during the spot-knocking process.
Moreover, the insulating layer between the gate electrode(s) and the substrate may be charged during use due to, for example secondary emission effects and may have a detrimental effect on the shape or direction of the emissive electron beam.